Monday 22 July 2013

Angling Myths No.1

This is the first in what may become an occasional series of angling myths.   Basically bits of information doing the rounds, based on either nothing at all, pure speculation, or on incomplete and inaccurate data.  All with the tag "in my opinion" of course.
So: number one.   "Fish cannot see red fishing  line".  
This was doing the rounds a while ago, and still persists  to an extent, mainly in some river fishing, barbel forums and probably elsewhere.  At least a couple of very successful anglers were touting this about, and using red braid on their reels. Practising what they preached of course, but did they have any basis for their thinking?   Well, sort of, but with some very inaccurately applied science. 
The colour red is absorbed more readily by water, becoming less and less intense as the water depth increases, and this effect can be seen quite clearly in all those underwater sea videos, where, unless the camera shot is close to the subject  the whole scene looks bluish.  It is bluish because the red end of the spectrum has been greatly absorbed compared to the blue end.  To get reef fish photographs in true colour it is often necessary to add artificial light before clicking the shutter.
So what happens with red line?   In shallow water, seen at close range by the fish, it remains red, limited absorption of any colour taking place.  At great distances and depths the red component of the line would no longer be visible, BUT the line would then look to be black.   Absence of red light does not mean that the line would then become invisible.  It simply means that there is no red light available to be reflected from the line.  If red light is the only colour to be reflected from that line in air, then in deep water, little red light remains to be reflected from the line. Any object emitting or reflecting no light, or very little light,  appears as black.
The only way to make line invisible in water is to make it from a clear, transparent and colourless material.   And then, additionally, to use a material that has, as far as is possible, the same refractive index as water.  Under those circumstances, light rays pass straight through the line, without being bent as they pass through the line.  In effect the line then appears not to be there.   And that is exactly what some modern lines try to do.  They try to eliminate the "bent stick" effect that you can easily see when you penetrate a water surface with a straight rod.  The rod appears bent, because the refractive index of air is different to that of water.   The objective therefore is to create a line without any of that bent stick effect. I understand lines which get near to this are called Fluorocarbons.   Such lines have their limitations, I am informed that they are usually stiffer than conventional lines,  and there is little advantage to use them as floating lines, because the meniscus effect will still allow them to be seen.
To those who might still subscribe to the invisible red line theory, I would say: "Take your red line, put it into the river.  Can YOU still see it?   Of course you can, and so can the fish."


  1. Of course the other thing to add to this is that our perceptions and their perceptions are going to be absolutely different. Fish have no way of knowing that line is any way linked with danger, whether it be red, black, clear of luminous green. They'll have to learn that by making mistakes.

    Trouble is, shoaling fish do not have to learn things individual by individual, but communicate danger throughout the shoal individual to whole shoal. Once one makes the association strongly enough, they're all spooked!

    Of course this is all pure conjecture. They may not be able to make sense of straight lines, for instance. Birds cannot fathom fast approaching objects such as cars — they'll see an object slowly expanding in size but expanding most rapidly into a very large danger signal only when very close, but it's too late to make sense of it afterwards !

  2. Hi Jeff, yes, I carefully avoided trying to interpret what the fish may THINK of these fishing lines. I would agree that their perceptions are going to be somewhat, rather than completely, different to our own. After all, we know exactly what line is. And do they ever actually learn to actively fear line, and associate it with capture, or will it always just be something different to their normal experience? Is a fish bright enough to LEARN from its interactions with tackle and bait, or is its reaction to danger merely one facet of its instinctive behaviour. I theorise that instinctive behaviour is knowledge built into the DNA, that codes for an area of pre-programmed brain. That instinct will cover swimming, feeding, perch, kingfishers, heavy splashes etc, but I would speculate that it might also cover "something is not quite right".

    I have often seen fish turn away from a hooked bait, but they did not usually do so fearfully. Even fish that brush the line with their bodies do not usually seem to do more than dodge around it, UNLESS that line itself moves and the fish feels the unexpected movement of that line.

    Shoaling fish: if one individual spooks, then understandably the rest will probably spook also, but they are unlikely to know why that first fish spooked. Being able to communicate danger relieves them of the need to learn quite so much as individuals. Yet: I often read of anglers being told to get the shoal of fish competing for the food. Often this is in heavily stocked waters, and, despite providing the fish with ample opportunities to learn that bait +line=danger, they seem not to get the message. It is almost as if they know that, to get their fair share of food, they must accept being caught occasionally.

    I have never hit a bird whilst driving myself (45 years), although I did hit a bat last year. Maybe the problem with fast moving cars is that birds never need to associate distant objects with danger. A peregrine 400 yards away is not a danger. Unfortunately cars move a lot quicker than any of their instinctive programming allows for. So birds get hit simply because they do not have time to react, nor the mental abilities needed to predict that a distant car will very soon be a nearby car. The local pigeons,(streetwise birds?) most of the time, seem to be able to avoid cars quite well though. They survive in unexpected numbers.

    Interesting about the straight lines, and although I realise it is something you conjured up purely as an example, I have watched carp this year, travelling in the mornings, to weedier feeding areas at the other end of a lake. They travelled in astonishingly straight lines, at the water surface, and I was concluding that they probably were using bankside markers, or maybe the sun, in order to maintain such direct lines, some of which were hundreds of yards long.

    So much on which to speculate!


    1. You mention peregrines. I was thinking of them and sparrowhawks too, just after posting my comment as examples of how a creature takes advantage of a weakness of perception. They both approach so quickly head on that the prey has no chance of seeing that tiny speck approaching enlarging into a danger signal until the very last fraction of a second before its demise.

      But, when it comes to an oblique view of an outline shape the prey are well aware.

      As an example of that. I witnessed a sparrowhawk just yesterday take off from the ground, exit through a bush and then cross open grassland accompanied by the alert calls of blackbirds. One had seen the danger immediately, let everyone else know just as quickly and they all called out in response!

      Shoaling behaviour perhaps?

  3. Always knew red went black under water, but not till past 50 feet or more. Could never work out why they made red line in the first place.

  4. Me neither Martin. Red is hardly a commonplace subsurface colour, even in shallow water. Same with "camouflaged" lines.
    ...And why can you not buy green maggots?

  5. Indeed. Green is the is very colour of caddis grubs. James Dennison was thinking of this recently, I've thought about it many times, but never acted on it.